1. Field of the Invention
The present invention relates to an information reading apparatus, a method of producing the apparatus, and a radiation imaging system using the apparatus and, more particularly, to an information reading apparatus having a wavelength conversion member such as a scintillator or the like, a production method of the apparatus, and a radiation imaging system using the apparatus.
2. Related Background Art
Under the trend toward filmless roentgenography, some companies have released semiconductor instruments provided with an X-ray area sensor in recent years, and methods thereof are generally classified under two types, a direct system (a type in which X-rays are directly converted into electric signals to be read) and an indirect system (a type in which X-rays are once converted into visible light and the visible light is then converted into electric signals to be read).
FIG. 1A is a schematic, cross-sectional view of an information reading device provided with an example of the X-ray area sensor of the indirect system. FIG. 1B is a schematic plan view of FIG. 1A. In FIGS. 1A and 1B, numeral 401 designates a glass substrate, 402 MIS photosensor portions using amorphous silicon, 403 TFT switch portions, 404 electrode portions (areas where electrodes are provided), 411 a first protective layer made of a nitride or the like for electrically protecting the photosensor portions 402, the TFT switch portions 403, etc., 412 a scintillator made of, for example, cesium iodide (CsI) as a wavelength conversion member, 413 a scintillator protecting layer made of an organic resin for protecting the scintillator 412 from external water or the like, 414 a reflective substrate with a high reflectance made of an aluminum sheet or the like, and 415 a second protective layer made of an organic substance such as polyimide (PI) or the like for protecting the photosensor portions 402 etc. from impurities in the scintillator 412.
When X-rays are incident from the upper part of FIG. 1A, the X-rays permeate the reflective substrate 414 and the scintillator protecting layer 413 to be absorbed by the scintillator 412. The scintillator 412 absorbing the X-rays emits visible light in all the directions in the bulk. At this time, since the crystals of the scintillator 412 are of the vertically grown columnar shape as illustrated in FIG. 1A, the light emitted in the bulk eventually travels in the longitudinal direction of the columnar shape with being reflected at grain boundaries, substantially according to the principle of light transmittance in optical fibers.
Then, most of the light is concentratedly guided to the photosensor portions 402 and TFT switch portions 403 in the lower part of FIG. 1A. Therefore, this structure is able to achieve a high sensitivity and improvement in resolution.
A production method of the information reading device as an X-ray area sensor illustrated in FIGS. 1A and 1B will be described below. The X-ray area sensor illustrated in FIGS. 1A and 1B is a semiconductor device obtained by forming the photosensor portions 402 and TFT switch portions 403 on the glass substrate 401, thereafter forming the first protective layer 411 thereon, and further forming the second protective layer 415 thereon. In this state the scintillator 412 is directly deposited onto the second protective layer 415 by vapor deposition while portions without necessity for the vapor deposition are preliminarily covered with a mask (not shown).
In order to make the scintillator 412 of the ideal columnar structure of cesium iodide, although the temperature during the vapor deposition is preferably not less than 200xc2x0 C., but the temperatures of not less than 200xc2x0 C. will deteriorate the photosensor portions 402 and the TFT switch portions 403 already formed, the scintillator 412 has to be formed at a temperature of not more than 200xc2x0 C.
After the formation of the scintillator 412 through the vapor deposition, a protective film for moisture resistance is bonded thereonto to form the scintillator protecting layer 413. An aluminum sheet as the reflective substrate 414 is then bonded thereonto, thus completing the X-ray area sensor.
When the scintillator 412 is formed in this way by directly depositing cesium iodide onto the glass substrate 401 having the photosensor portions 402 and TFT switch portions 403 formed thereon, the optically advantageous structure can be provided, but on the other hand the temperature has to be kept not more than 200xc2x0 C.
This means that, where the photosensor portions 402 and TFT switch portions 403 are formed of amorphous silicon, optimization has to be implemented within the temperature range such that hydrogen atoms do not become unbound.
FIGS. 2A and 2B are a schematic plan view and a schematic, cross-sectional view of a large information reading device, for example, provided with four area sensors, which are the semiconductor devices illustrated in FIGS. 1A and 1B. In the information reading device illustrated, the four area sensors are bonded onto the substrate 605 (arranged adjacent to one another) and the scintillator 412 is directly deposited onto them. The four area sensors are fixed on the substrate 605 through an adhesion layer 606.
For this structure, a gap 650 is created between adjacent area sensors as illustrated in FIG. 2A and the plane of the vapor deposited surfaces of the scintillator is divided near the gap; therefore, the scintillator 412 also grows in the lateral direction in the figure. The crystals of the scintillator near the gap 650 are not formed in the shape of columns perpendicular to the second protective layer 415 when compared with those in the other portions, accordingly.
FIGS. 3A and 3B show another information reading device provided with an area sensor which has a glass substrate 401 having photosensor portions 402 and TFT switch portions 403 formed on a surface thereof, and a scintillator 412 of the optimum columnar structure provided on the surface.
In FIGS. 3A and 3B, numeral 511 designates a protective layer made of, for example, a nitride or the like for protecting the photosensor portions 402, etc. from external water, 512 an adhesion layer for bonding the scintillator 412 and the protective layer 511 to each other, and 515 a seal portion made of an organic resin. Members similar to those illustrated in FIGS. 1A and 1B are denoted by the same reference numerals.
In the information reading device illustrated in FIGS. 3A and 3B, the scintillator 412 is vapor deposited on the reflective substrate 414. The photosensor portions 402, etc. and the protective layer 511 are formed on the glass substrate 401 to obtain a semiconductor device, and the scintillator 412 is bonded onto the protective layer 511 through the adhesion layer 512. In the last step, the scintillator 412 and the adhesion layer 512 are sealed by a sealant 515.
When the part of the reflective substrate 414 and the part of the glass substrate 401 are bonded to each other in this way, it becomes feasible to form the scintillator 412 on the reflective substrate 414 without care on deterioration of the photosensor portions 402, etc. due to the temperature during the vapor deposition of the scintillator 412, and thus to obtain the ideal columnar structure. However, since cesium iodide as the material of the scintillator 412 is brittle, it is necessary in this structure to pay close attention so as not to break the scintillator 412 when bonding the scintillator 412 and the protective layer 511 to each other.
As described above, the information reading device illustrated in FIGS. 3A and 3B was fabricated by bonding the scintillator and the protective layer to each other, and the scintillator was sometimes broken in part in the bonding. The reason is that cesium iodide for forming the scintillator is brittle as described above.
Further, there were desires for further improvement in the sensitivity of the information reading device illustrated in FIGS. 3A and 3B. It is necessary herein to decrease the thickness of the reflective substrate in order to improve the sensitivity. This is because the reflective substrate absorbs incident X-rays or the like and the reflective substrate, if it is thick, decreases the quantity of X-rays reaching the wavelength conversion member such as the scintillator or the like. However, with decrease in the thickness of the reflective substrate, the scintillator was sometimes split or broken during the bonding between the protective layer and the reflective substrate, or the scintillator itself was crumpled in certain cases.
In the case of the information reading devices illustrated in FIGS. 1A and 1B and in FIGS. 2A and 2B, since the scintillator was directly vapor deposited onto the second protective layer having the amorphous silicon elements formed thereon, there was the limitation of use temperature because of the weakness of amorphous silicon to high temperatures as described above, and there was the problem that the scintillator was not allowed to be formed at the temperature suitable for obtaining the ideal columnar structure for the scintillator.
Further, with the incidence of X-rays on the information reading device as illustrated in FIGS. 2A and 2B, the sensitivity to X-rays is uneven and thus unpreferable near the gap 650, because the shapes of the crystals of the scintillator are not columnar there. Therefore, there were desires for improvement therein.
An object of the present invention is to provide an information reading apparatus capable of preventing the scintillator from being broken during the bonding of the scintillator to the device-side surface, and a radiation imaging system having it.
Another object of the present invention is to provide an information reading apparatus improved in the sensitivity throughout the entire image-receiving area, and a radiation imaging system having it.
Still another object of the present invention is to provide an information reading apparatus capable of reading information with higher quality and without unevenness of sensitivity throughout the entire image-receiving area, and a radiation imaging system having it.
Another object of the present invention is to provide a production method involving no breakage of the wavelength conversion member such as the scintillator or the like.
According to a first aspect of the present invention, there is provided an information reading apparatus comprising a first substrate having a wavelength conversion member formed thereon and a second substrate having a photoelectric conversion portion formed thereon, the first and the second substrates being bonded to each other through an adhesive, wherein a protective layer is formed so as to cover the wavelength conversion member on the first substrate.
According to a second aspect of the present invention, there is provided an information reading apparatus comprising a wavelength conversion means having a wavelength conversion member provided on a substrate, a sensor substrate having a plurality of photoelectric conversion elements arranged on a substrate, and a buffer layer provided between the wavelength conversion member and the photoelectric conversion elements.
According to a third aspect of the present invention, there is provided an information reading apparatus comprising a wavelength conversion means having a wavelength conversion member and a buffer layer provided in the mentioned order on a substrate and a sensor substrate having a plurality of photoelectric conversion elements provided on a substrate, the wavelength conversion means and the sensor substrate being bonded to each other such that a protective layer is located on the side of the wavelength conversion member.
According to a fourth aspect of the present invention, there is provided a radiation imaging system comprising the information reading apparatus described above, a signal processing means for processing a signal from the information reading apparatus, a display means for displaying a signal from the signal processing means, and a radiation source for irradiating the information reading apparatus with radiation.
According to a fifth aspect of the present invention, there is provided a method of producing an information reading apparatus comprising preparing a substrate having a wavelength conversion member and a resin layer in an outermost surface, applying an adhesive to a sensor substrate provided with a photoelectric conversion element, and then bonding the substrate and the sensor substrate to each other such that the wavelength conversion member is located on the adhesive side.